<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <style>
        * {
            list-style: none;
            margin: 0;
            padding: 0;
        }

        ul {
            width: 600px;
            height: 600px;
            border: 3px solid rebeccapurple;
            font-weight: bold;
            color: white;
            text-align: center;
            line-height: 100px;
            font-size: 40px
        }

        /* li:nth-child(even) {
            background-color: red;
        }

        li:nth-child(odd) {
            background-color: #000000;
        } */

        li:nth-child(1){
            grid-area: header;
            background-color: red;
        }
        li:nth-child(2){
            grid-area: left-sidebar;
            background-color: green;
        }
        li:nth-child(3){
            grid-area: right-sidebar;
            background-color: green;
        }
        li:nth-child(4){
            grid-area: bottom;
            background-color: black;
        }

        ul{
            display: grid;
            grid-template-rows: repeat(3,1fr);
            grid-template-columns: repeat(3,1fr);
            grid-template-areas: 
            "header header header"
            "left-sidebar . right-sidebar"
            "bottom bottom bottom"
            ;
        }
    </style>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
    </ul>
</body>

</html>